The evolution of chemical and microbiological properties of fresh goat milk cheese during its shelf life

摘要

This study investigated the changes in chemical and microbiological properties of fresh goat milk cheese stored in an open deck refrigerated display cabinet (6 ± 2℃) or in a dark cold room (4 ± 1℃). The effects of partial-vacuum packaging and fluorescent lighting were studied during the cheese shelf life (45 d) and 15 d after. Storage conditions did not affect the pH values (4.3), whereas a slight decrease in moisture (ca. 1%) and in water activity (<0.01 units) was recorded. Proteolysis monitored by Kjeldahl determination increased significantly during storage of all samples. The highest increase from 8.5 to 13.0% of soluble nitrogen (expressed as percentage of total nitrogen) was measured in cheese packaged in the presence of air and stored in a lighted cabinet. The proteolytic trend was also studied through capillary zone electrophoresis by monitoring the degradation of the main casein fractions and the formation of new peptides. In particular, 2 indices, based on peak area ratio of new-formed peptides and casein fractions were related to cheese age. Lipolysis, measured by solid-phase microextraction gas chromatography coupled to mass spectrometry of volatile fatty acids, was unaffected by air or light and did not proceed through storage. As expected, hexanal formed mainly in cheeses stored under light and packaged in air. Evaluation of sensorial quality, performed using a hedonic scale, showed significantly lower scores of cheeses kept under light compared with those kept in the dark, both at 45 and 60 d storage. Overall, the microbiological and chemical results suggested that the shelf life of soft goat milk cheese would be extended from 45 to 60 d. Such conclusion was supported also by the sensory quality evaluation.